1. Field of the Invention
The present invention relates to an exposure method and an exposure apparatus, and more particularly, to an exposure method and an exposure apparatus used when a mask pattern is transferred onto a light-sensitive substrate during a photo lithography process for producing semiconductor devices, image pickup devices (CCDs etc.). liquid crystal display devices, plasma displays, thin film magnetic heads and the like. The present invention is suitably used for the exposure apparatus using ultraviolet light such as an excimer laser or the like as an exposure beam.
2. Description of the Related Art
As an integrated circuit is further reduced in size, in a full field exposure type projection exposure apparatus such as a stepper or a scan and exposure type projection exposure apparatus such as a step-and-scan apparatus, it is required to enhance resolution. One method for enhancing the resolution is to shorten the wavelength of illumination light (exposure light) for exposure. For this reason, the wavelength of exposure used for a projection exposure apparatus is shortened year after year. The currently mainstream exposure light is KrF excimer laser light (wavelength of 248 nm). At the present, ArF excimer laser light (wavelength of 193 nm) of shorter wavelength and F2 laser light (wavelength of 157 nm) are also under test. Harmonics of metal vapor laser light and YAG laser light and the like are also under test.
As excimer laser light sources used as exposure light sources, there are a narrow-band laser light source in which the full width at half maximum of a spectrum of the laser light is 2 to 3 pm or smaller, and a broadened-band laser light source in which the full width at half maximum of a spectrum of the laser light is 100 pm or more. When illumination light having short wavelength equal to or shorter than ultraviolet region such as excimer laser light is used as exposure light, only quartz (SiO2) and fluorite (CaF2) are presently known as a glass material for refractor having practical transmittance, and the narrow-band laser light source has an advantage of being easy to carry out achromatization of a projection optical system as compared with the broadened-band laser light source. However, the band of the excimer laser light is originally broadened band, and in order to use the excimer laser as the narrow-band laser light source, it is necessary to carry out injection-locking or the like for narrowing the band of the oscillation spectrum, and the broadened-band laser light source has advantages in terms of laser output, durability (life), and manufacturing cost. Therefore, attempts are recently made for the projection optical system to have a structure in which achromatization is easily carried out, so that the broadened-band laser source can be used.
That is, as a projection optical system used for a projection exposure apparatus, there are a refracting-type projection optical system comprised of a plurality of refractors alone, and a catadioptric projection optical system such as disclosed in Japanese Patent Application Laid-open No. 6-132191 comprising a combination of a catadioptric element such as a concave mirror and refractors. In the former refracting projection optical system, a proportion of lenses made of fluorite is increased to broaden an achromatic width, thereby making it possible to use the broadened-band laser light source. In the latter catadioptric projection optical system, since the concave mirror disposed between the refractors has no chromatic aberration and it is easy to achromatize, and it is possible to use the broadened-band laser light source.
In recent years, a pattern steps tends to move from on the order of conventional 1 xcexcm to 0.1 xcexcm or less with CMP technique (Chemical Mechanical Polishing) which flattens a surface of a wafer. A film thickness of a resist can also be made thinner in accordance with this trend. Therefore, when a projection optical system having the numerical aperture of 0.7 or more is used for example, it is possible to obtain a resolution of about 80 to 130 nm. In the case of the catadioptric projection optical system, if a narrow-band ArF excimer laser light having a full width at half maximum of about 0.5 to 1 pm is used for example, it has been found that it is possible to design an optical system having a maximum effective field diameter of a lens of about 300 mm and numerical aperture of 0.7 or more by using several aspheric optical elements.
As described above, laser light in a far ultraviolet region such as an ArF excimer laser is used in a recent projection exposure apparatus so as to enhance the resolution. However, ultraviolet light is originally absorbed by ozone (O3) and if the wavelength becomes about 200 nm or shorter, the absorption amount of the light by oxygen (O2) is increased. Thereupon, when the laser light of such an ultraviolet region is used, it is preferable that a gas having a low absorptance with respect to ultraviolet light and having no effect on photoresist such as an ozone-free air or a nitrogen (N2) gas is circulated on the optical path in the illuminating optical system or projection optical system to suppress the reduction in exposure amount. However, since the nitrogen gas has a high index of refraction, when the nitrogen gas is circulated in the projection optical system, the index of refraction is varied by a slight variation in temperature or pressure and the projection image is wandered, resulting in an inconvenience that the exposure precision (superposing precision or the like) is lowered. Especially in a catadioptric projection optical system designed to have a numerical aperture of 0.7 or greater, even though the number of lenses is as small as 15 to 25, since a distance between a reticle and a wafer is long, space between lenses is great, and a wandering effect on the projection image due to temperature variation is increased.
In order to suppress the wandering of the projection image, it is effective that a gas such as helium (He) having a small index of refraction as small as about xe2x85x9 of that of nitrogen gas and having small variation amount thereof is circulated in the projection optical system. However, the projection optical system is provided with a driving mechanism for driving predetermined lens or the like for excellently keeping the image-forming characteristics, and with an opening for bringing in and out an optical filter or the like which was optimized with respect to the pattern shape. Since inside and outside of the projection optical system are not completely insulated from each other, it was difficult to constantly keep purity of the helium gas in the projection optical system and to maintain excellent image-forming characteristics. Further, it may be possible to keep supplying helium gas so that the pressure of the helium gas becomes positive pressure with respect to the pressure outside the projection optical system, thereby constantly keeping the purity of the helium gas in the projection optical system. However, since the helium gas is expensive under present circumstances, there is an inconvenience that if the flow rate of the helium gas is increased in this manner, working cost is increased.
In view of the above circumstances, it is a first object of the present invention to provide an exposure method capable of suppressing deterioration in image-forming characteristics due to variation in a temperature or a purity of a gas in a projection optical system, and capable of maintaining excellent image-forming characteristics. It is a second object of the present invention to provide an exposure method capable of preventing the transmittance of an exposure beam in a projection optical system from being lowered, or capable of suppressing the deterioration in image-forming characteristics. Further, it is another object of the present invention to provide an exposure apparatus capable of carrying out the above-described exposure methods.
According to a first aspect of the present invention, there is provided an exposure method, comprising:
irradiating a pattern of a mask with an exposure beam to expose an image of the pattern of the mask onto a substrate through a projection optical system, there being provided an image-forming characteristics control member which controls predetermined image-forming characteristics of the projection optical system by driving a predetermined optical member in the projection optical system, and an isolating member which isolates the image-forming characteristics control member from outside air of the projection optical system, and
supplying a gas through which the exposure beam is allowed to pass into the isolating member and around the optical member during the exposure.
According to the above-mentioned exposure method according to the first aspect of the present invention, air-tightness of the interior of the projection optical system is enhanced by providing the isolating member which isolates the image-forming characteristics control member which controls the predetermined image-forming characteristics of the projection optical system from outside air of the projection optical system. Therefore, when a gas through which the exposure beam is allowed to pass is supplied to the inside of the isolating member and around the optical member during exposure, a variation in a temperature of a purity of the gas in the projection optical system is reduced, and as a result, it is possible to suppress the deterioration of the image-forming characteristics and to maintain the excellent image-forming characteristics.
According to a second aspect of the present invention, there is provided an exposure method wherein a pattern of a mask is irradiated with an exposure beam to expose an image of the pattern of the mask onto a substrate through a projection optical system, comprising:
supplying a gas through which the exposure beam is allowed to pass to at least a portion of an optical path of the exposure beam in the projection optical system,
detecting at least one of a purity and a temperature of the gas in the projection optical system, and
maintaining at least one of the purity and the temperature of the gas in the projection optical system within a predetermined tolerance range based on a result of the detection.
According to the above-mentioned exposure method according to the second aspect of the present invention, at least one of the purity and the temperature of the gas having an excellent transmittance in the projection optical system is substantially continuously measured, that is, at least one of them is successively measured at a predetermined sampling rate for example, and based on a result of this measurement, at least the one of the purity and the temperature is continuously maintained within the predetermined tolerance range. Therefore, it is possible to prevent transmittance from being lowered with respect to the exposure beam in the projection optical system, or to suppress the deterioration of the image-forming characteristics. Further, when the temperature of the gas is adjusted, it is possible to collect heat generated by exposure by utilizing the gas as a heat exchange medium, and it is also possible to adjust a temperature in the projection optical system.
According to a third aspect of the present invention, there is provided an exposure apparatus which irradiates a pattern of a mask with an exposure beam to exposure an image of the pattern of the mask onto a substrate through a projection optical system, comprising:
an image-forming characteristics control member which controls predetermined image-forming characteristics of the projection optical system;
an isolating member which isolates the image-forming characteristics control member from outside air of the projection optical system; and
a gas supply system which supplies a gas through which the exposure beam is allowed to pass into the isolating member and around the optical member.
According to the above-mentioned exposure apparatus according to the third aspect of the present invention, the exposure method according to the first aspect of the present invention can be carried out, and exposure with high precision can be performed with the deterioration being suppressed of the image-forming characteristics that may be caused due to variation in a temperature or a purity of a gas in a projection optical system.
According to a fourth aspect of the present invention, three is provided an exposure apparatus which irradiates a pattern of a mask with an exposure beam to expose an image of the pattern of the mask into a substrate through a projection optical system, comprising:
a gas supply apparatus which supplies a gas through which the exposure beam is allowed to pass to at least a portion of an optical path of the exposure beam in the projection optical system; and
a sensor which substantially continuously detects at least one of a purity and a temperature of the gas in the projection optical system, wherein
the gas supply apparatus is driven based on a detection result of the sensor to maintain at least one of the purity and the temperature of the gas in the projection optical system within a predetermined tolerance range. With this exposure apparatus, the exposure method according to the second aspect of the present invention can be carried out.
According to a fifth aspect of the present invention, there is provided an exposure apparatus which irradiates a mask with an exposure beam emitted from a light source to expose a substrate with the exposure beam through the mask, comprising:
an adjustment apparatus which moves at least one optical element in an optical system disposed between the light source and the substrate to adjust optical characteristics of the optical system;
an isolating member which isolates at least a portion of the adjustment apparatus from outside air; and
a gas supply system which supplies a gas through which the exposure beam is allowed to pass into the isolating member. With this exposure apparatus, the exposure method according to the first aspect of the present invention can be substantially carried out.
According to a sixth aspect of the present invention, there is provided a method for manufacturing a device, comprising:
a step of transferring a device pattern (mask pattern) onto a work piece (substrate) using the exposure method according to the first or second aspect of the present invention.
According to a seventh aspect of the present invention, there is provided an exposure apparatus which irradiates a mask with an exposure beam emitted from a light source to expose a substrate with the exposure beam through the mask, comprising:
a driving mechanism which drives at least one optical element in an optical system disposed between the light source and the substrate;
a gas supply system which supplies a gas through which the exposure beam is allowed to pass to an optical path in the optical system; and
a gas discharge system which discharges the gas supplied into the optical system through a periphery of the driving mechanism.
According to a eighth aspect of the present invention, there is provided an exposure apparatus which irradiates a mask with an exposure beam emitted from a light source to expose a substrate with the exposure beam through the mask, comprising:
a driving mechanism which drives at least one optical element in an optical system disposed between the light source and the substrate, and
a cover which cuts off communication established by the driving mechanism between an interior of the optical system and outside air of the optical system.
According to a ninth aspect of the present invention, there is provided an exposure method wherein a mask is irradiated with an exposure beam emitted from a light source to expose a substrate with the exposure beam through the mask, comprising:
supplying a gas through which the exposure beam is allowed to pass to an optical path in an optical system disposed between the light source and the substrate, and
discharging the gas through a periphery of a driving mechanism which drives at least one optical element in the optical system.
According to a tenth aspect of the present invention, there is provided a manufacturing method for an exposure apparatus wherein a mask is irradiated with an exposure beam emitted from a light source to expose a substrate with the exposure beam through the mask, comprising:
disposing at least one optical element in an optical system disposed between the light source and the substrate in a lens barrel,
disposing a driving mechanism which drives the optical element on a side face of the lens barrel, and
mounting a cover which covers at least a portion of the driving mechanism on the side face of the lens barrel.